Method and apparatus for achieving fast reconnection of permanent virtual channels in a frame relay network

ABSTRACT

Rapid reestablishment of permanent virtual circuits (PVCs 15 1 -15 6 ) between frame relay switches 12 1 -12 4  in a frame relay ( 10 ) is accomplished by periodically polling the switches by a configuration controller ( 18 ) via an out-of-band connection to obtain PVC information from the switches. Should a fault occur, the fault is isolated and mitigated. Thereafter, the configuration controller ( 18 ) downloads the stored PVC information to the switches in parallel via the out-of-band connection to enable the switches to re-establish the PVCs quickly, rather than wait to do so via an in-band connection.

TECHNICAL FIELD

[0001] This invention relates to a technique for re-establishingpermanent virtual circuits in a frame relay network in a rapid andefficient manner following a service outage.

BACKGROUND ART

[0002] Presently, several inter-exchange telecommunications carriers,such as AT&T, offer frame relay service for transporting data packetsfrom one local area network to another. Among the customers that utilizeframe relay service from AT&T and other telecommunications carriers arebanks and financial institutions that transport data from automatedteller machines and point of service terminals to data processingfacilities to enable debiting of a purchaser's account for cashwithdrawals and debit-card purchasers. Other customers of frame relayservice include manufacturers that use the service to transmit dataamong manufacturing facilities to coordinate scheduling, inventorylevels, and other activities. Large retailers who maintaingeographically separated stores and warehouses also use frame relayservice to exchange data between facilities to assure timely delivery ofmerchandise.

[0003] The heavy reliance of customers on such frame relay servicemandates that the carriers that offer such service provide fastrestoration in the event of a service outage. Unfortunately, present daytechniques for restoring service often take a significant amount oftime, especially for very large networks. Invariably, in the event of aservice outage, all of the Permanent Virtual Circuits (PVCs) that linkframe relay switches become disabled, and must be re-established afterisolation and repair of the fault. Reconnection of the PVCs requiresre-establishment of logical (control) signaling links among the framerelay switches first before the frame relay switches can re-establishthe PVCs themselves. During normal operation of a frame relay network,establishing such logical signaling links takes little time. However, inthe event of a large service outage, a significant amount of activityoften exists in the network, significantly lengthening the time requiredto re-establish the PVCs among the frame relay switches. As aconsequence, customers incur delayed restoration of service, increasingcustomer dissatisfaction and reducing revenue to the carrier providingsuch service.

[0004] Thus, there is a need for a technique that reduces the timerequired to re-establish PVCs in a frame relay network following aservice outage.

BRIEF SUMMARY OF THE INVENTION

[0005] Briefly, in accordance with a preferred embodiment of theinvention, a method is provided for restoring Permanent Virtual Circuits(PVCs) that link frame relay switches in a frame relay network followinga fault. Prior to the fault, a main configuration controllerperiodically polls each of the switches in the frame relay network toobtain information about the PVCs linking the switches. Such polling isdone out-of band from the frame relay network, either via a dedicated IPcontrol network, or via dial-up links of a Public Switched TelephoneNetwork. The main configuration controller stores the informationobtained during each polling by over-writing the information obtainedduring the previous polling. Following isolation and mitigation of afault in the frame relay network, the main configuration downloads toeach switch, via the out-of-band network, the stored PVC information toenable the frame relay switches to the switches to re-establish the PVCsquickly.

BRIEF DESCRIPTION OF THE DRAWING

[0006]FIG. 1 shows a block schematic diagram of a frame relay network inaccordance with a preferred embodiment of the invention.

DETAILED DESCRIPTION

[0007]FIG. 1 illustrates a frame relay network 10 in accordance with apreferred embodiment of the invention. The network 10 includes aplurality of frame relay (FR) switches, such as the switches 12 ₁-12 ₄.While the network 10 of the preferred embodiment includes the fourswitches, the network 10 could include a larger or smaller number ofswitches as required. The switches 12 ₁-12 ₄ each receive packet datafrom a corresponding one eof routers 13 ₁-13 ₄ that each serve one ormore data source/destinations 14—14. The frame relay switches 12 ₁-12 ₄are linked to each other via permanent virtual circuits (PVCs) 15 ₁-15 ₆in the manner shown in FIG. 1. The PVCs circuits 15 ₁-15 ₆ are akin toleased or private lines in a conventional Public Switched telephonenetwork in that the PVCs do not require reestablishment for everysubsequent transmission of data between a pair of frame relay switches.During normal operation, the frame relay switches 12 ₁-12 ₄ each storeinformation regarding the PVCs 15 ₁-15 ₆, especially those originatingat that switch within an image table (not shown). The image tableinformation enables to switch to know what PVC's exist for that switch,thus enabling the switch to send data without first having to establisha PVC for transmission.

[0008] In the event of a network outage, one or more of the PVCs maybecome inoperative. Indeed, a large service outage may affect all or amajority the PVCs 15 ₁-15 ₆. At the present time, reestablishment of thePVCs 15 ₁-15 ₆ may consume significant time, especially following alarge service outage. To re-establish the PVCs 15 ₁-15 ₅, the framerelay switches 12 ₁-12 ₄ must first reestablish signaling links 16 ₁-16₆, (shown by dashed lines), whereupon the frame relay switchesthereafter proceed to set up the PVCs 15 ₁-15 ₆ While the time requiredto set up the PVCs 15 ₁-15 ₆ during normal operation is generally minor,after a major service outage, an extraordinary amount of activitytypically exists on the frame relay network, significantly lengtheningthe time required to reestablish the PVCs.

[0009] In accordance with the invention, the time required to set up thePVCs' 15 ₁-15 ₆ can be reduced by communicating PVC information to theframe relay switches 12 ₁-12 ₄ out of band, i.e., via a channel that isseparate and distinct than the PVCs 15 ₁-15 ₆ and the control channels16 ₁-16 ₆. To accomplish such out-of-band communication of PVCinformation, the network 10 of the invention includes a mainconfiguration controller 18, and preferably, a back-up configurationcontroller 20. A control network 22 that is out-of-band with respect tothe PVCs 15 ₁-15 ₆ and the signaling links 16 ₁-16 ₆ couples the mainand back-up configuration controllers 18 and 20, respectively, to a mainadministration port 24, and preferably, a back-up administration port 26as well. The control network 22 may comprise a dedicated data network,such as a network that uses an IP protocol. Alternatively, the network22 could comprise a Public Switched Telephone Network (PSTN), such asthe PSTN maintained by AT&T. When the network 22 comprises a PSTN, theconnections between the PSTN and the main and back-up configurationcontrollers 18 and 20, respectively, and the main and back-upadministrative ports 24 and 26, respectively, may comprise dedicatedlines or dial-up links. The main administrative port 24 has connections28 ₁-28 ₄ to the frame relay switches 12 ₁-12 ₄, respectively, whereaseach of the connections 30 ₁-30 ₄ links a corresponding one of the framerelay switches to the back-up administrative port 26. Each of theconnections 28 ₁-28 ₄ and 30 ₁-30 ₄ typically has a T3 bandwidth andserves to communicate PVC information between each switch and acorresponding one of the main and back-up administration ports 224 and26.

[0010] In operation, the main controller 18 periodically polls each ofthe frame relay switches 12 ₁-12 ₄ via the main administrative port 24(or in the event of its failure, via the back-up administrative port 26)to obtain information regarding the cross connects, that is the PVCs 15₁-15 ₆, that exist between switches. Depending on the size of the framerelay network, and the frequency at which PVC changes occur, the mainconfiguration controller 18 may poll the switches as often as everyhour, or as infrequently as once each day. The main configurationcontroller 18 obtains the PVC information from the frame relay switches12 ₁-12 ₄ out-of-band, that is separate from the PVCs 15 ₁-15 ₆ and thecontrol links 16 ₁-16 ₆, by making use of the out-of-band controlnetwork 22. The main configuration controller 18 stores the PVCinformation obtained during each subsequent polling by overwriting theinformation obtained during the last previous polling. As the mainconfiguration controller 18 stores the most recently obtained pollinginformation, main configuration controller provides the information tothe back-up configuration controller 20 via the network 22. In this way,the PVC information stored at the back-up configuration controller 20mirrors the PVC information stored at the main configuration controller18.

[0011] Should the frame relay network 10 suffer a fault, thoseresponsible for maintaining the network will to isolate and mitigate thefault. After fault isolation and mitigation, the main configurationcontroller 18 (or in the event of its failure, the back-up configurationcontroller 20) downloads to each of the frame relay switches 12 ₁-12 ₄the PVC information for that switch based on the last polling. Inpractice, the main configuration controller 18 downloads the PVCinformation to the frame relay switches 12 ₁-12 ₄ in parallel, thusenabling the switches to receive the information quickly, and thereaftercommence restoration of the PVCs, rather than wait to communicate theinformation among themselves in-band, as occurred in the prior art. Thereceipt of the PVC information from the main configuration controller 18(or in the event of its failure, from the back-up configurationcontroller 20) out-of-band thus enables the frame relay switches tore-establish the PVCs 15 ₁-15 ₆ more quickly, reducing the interval ofcustomer outage, and the accompanying customer dissatisfaction.

[0012] In practice, the PVC information downloaded from the mainconfiguration controller 18 may not reflect the latest cross-connectioninformation at the frame relay switch, especially if new cross-connectshave been added since the last polling. We assume the frame relayswitches 12 ₁-12 ₄ have the capability of comparing the downloaded PVCinformation from the main configuration controller 18 to the PVCinformation stored by the switch in its image table. Assuming that theswitches also have the ability of reconnecting/disconnecting its PVCs,then each switch can advantageously make the comparison between thedownloaded PVC information, and the PVC information in its image table,and thereafter make the necessary re-connections/disconnections inaccordance with the comparison.

[0013] The foregoing describes a technique for establishing rapidreconnection of permanent virtual circuits in a frame relay network.

[0014] It is to be understood that the above-described embodiments aremerely illustrative of the principles of the invention. Variousmodifications and changes may be made thereto by those skilled in theart which will embody the principles of the invention and fall withinthe spirit and scope thereof.

What is claimed is:
 1. A method for restoring Permanent Virtual Circuits(PVCs) linking frame relay switches in a frame relay network followingisolation and mitigation of a fault, comprising the steps of: prior tooccurrence of the fault, periodically polling each of the frame relayswitches via an out-of-band connection with respect to the PVCs by amain configuration controller to collect information from each switchregarding its PVCs; storing at the main configuration controller the PVCinformation for each switch obtained from each polling operation tooverwrite the stored PVC information obtained from a previous pollingoperation; and following isolation and mitigation of a fault,downloading the stored polling information from the main configurationcontroller to each corresponding frame relay switch via the out-of-bandconnection to cause each switch to reconnect the PVCs in accordance withthe downloaded PVC information.
 2. The method according to claim 1further including the steps of: storing at each switch prior to theoccurrence of a fault, an image table indicative of the PVCs originatingat said switch; following receipt of the downloaded PVC informationreceived at said switch, comparing the PVCs indicated by said downloadedinformation to the PVCs indicated by said image table; and effecting achange in any PVC specified in said image table that differs from saiddownloaded PVC information.
 3. The method according to claim 1 whereinthe frame relay switches are downloaded in parallel.
 4. The methodaccording to claim 1 wherein the polling step includes the step ofcommunicating information between each frame relay switch and theconfiguration controller via a dedicated Internet Protocol network thatis out-of-band with respect to PVCs of the frame relay network.
 5. Themethod according to claim 1 wherein the polling step includes the stepof communicating information between each frame relay switch and theconfiguration controller via a link of a Public Switched Telephonenetwork that is out-of-band with respect to PVCs of the frame relaynetwork.
 6. The method according to claim 1 including the steps ofstoring, at a back-up configuration controller the PVC informationobtained by polling each switch; and downloading from the back-upconfiguration controller to each switch the stored PVC information inthe event of a failure of the main configuration controller.
 7. A framerelay network comprising: a plurality of frame switches linked to eachother via Permanent Virtual Circuits (PVCs); a main administrative portcoupled to the frame relay switches; a main configuration controller for(a) periodically polling each of the frame relay switches to collectinformation from each switch regarding its PVCs, (b) storing the PVCinformation for each switch obtained from each polling operation tooverwrite stored PVC information obtained from a previous pollingoperation; and (c) downloading the stored polling information to eachcorresponding frame relay switch following isolation and mitigation of afault to cause each switch to reconnect the PVCs in accordance with thedownloaded PVC information; a control network for providing an out-ofband link between the main configuration controller and the mainadministrative port with respect to the PVCs linking the frame relayswitches.
 8. The network according to claim 7 further including aback-up configuration controller for receiving from the mainconfiguration controller the stored polling information and fordownloading the stored polling information to each corresponding framerelay switch following isolation and mitigation of a fault to cause eachswitch to reconnect the PVCs in accordance with the downloaded PVCinformation upon a failure of the main configuration controller.
 9. Thenetwork according to claim 7 wherein the control network comprises adedicated IP network.
 10. The network according to claim 7 wherein thecontrol network comprises a Public Switch Telephone Network having aplurality of dial up links, each connected to a separate frame relayswitch.
 11. The network according to claim 7 further including a back-upadministration port for coupling the main configuration controller tothe frame relay switches in the event of a failure of the mainadministration port.